1. Field of the Invention
The present invention relates to the improvement of an electric-discharge surface treatment method in which pulsed electric discharge is generated between an electrode and a material to be treated, and a hard coating comprising an electrode material or a substance formed by the reaction of the electrode material in response to the electric discharge energy is formed on the surface of the material to be treated. The invention further relates to the improvement of an apparatus and an electrode for carrying out the method.
2. Description of the Related Art
There has been already known a technique in which the surface of a metal material is coated by in-liquid electric discharge so that corrosion resistance and abrasion resistance are given to the metal material. The main point of the technique is as follows. That is, in-liquid electric discharge is performed with an electrode compression-molded out of a mixture of powder of tungsten carbide WC and cobalt Co, so that the electrode material is deposited on a material to be treated. Then, remelting electric-discharge treatment is performed with another electrode such as a copper electrode, a graphite electrode, or the like, so that higher hardness and higher adhesion force are obtained.
Description will be made below about the aforementioned conventional technique with reference to FIG. 5. Electric-discharge treatment is performed in liquid by use of a compressed tungsten carbide-cobalt WCxe2x80x94Co mixture powder electrode, so that tungsten carbide-cobalt WCxe2x80x94Co is deposited (primary treatment). Next, remelting treatment (secondary treatment) is performed with an electrode""such as a copper electrode which is not consumed so much. With the deposition in the primary treatment, the structure has a Vickers hardness of about Hv=1,410 and has many cavities. However, with the remelting treatment in the secondary treatment, the cavities in the coating layer are eliminated, and the hardness is also improved to be Hv=1,750.
According to this method, a coating layer which is hard and excellent in adhesion can be obtained for a steer material, but, for the surface of a sintered material such as sintered hard alloy, it is difficult to form a coating layer having a solid adhesion force.
However, through the research of the present inventors, it was proved that if a material such as titanium Ti or the like, for forming hard carbide, was used as an electrode and electric discharge was generated between the electrode and a metal material as a material to be treated, a solid hard film could be formed, without any process of remelting treatment, on the metal surface which was the material to be treated. It is understood that this was because the electrode material consumed by the electric discharge reacted with carbon C which was a component of treatment liquid so that titanium carbide TiC was produced. Further, it was proved that when a compressed powder electrode of metal hydride such as titanium hydride TiH2, or the like, was used, and electric discharge was generated between the electrode and a metal material which was a material to be treated, a hard film could be formed more quickly and more excellent in adhesion than in the case where a material such as titanium Ti, or the like, was used. Further, it is known that if a compressed powder electrode in which hydride such as titanium hydride TiH2 or the like is mixed with another metal or ceramic, is used, and electric discharge is generated between the electrode and a metal material which is a material to be treated, a hard coating having various properties with respect to the hardness, abrasion resistance, etc. can be formed quickly. This method is disclosed in JP-A-9-192937.
According to the aforementioned background-art electric-discharge surface treatment method, the material of an electrode reacts with carbon C formed by decomposition of a component of the treatment liquid by heat due to electric discharge so that a hard carbide coating is formed on a material to be treated. In this method, however, there has been a problem that the quantity of carbon C to be supplied has a limit so that the hardness of the coating does not increase satisfactorily.
The present invention was achieved to solve the foregoing problems. It is an object of the present invention to provide an electric-discharge surface treatment method for enhancing the hardness of a hardcoating formed on a material to be treated; and an apparatus and an electrode for carrying out the method.
In addition it is another object of the present invention to provide an electric-discharge surface treatment method which uses water carefree with fire; and an apparatus and an electrode for carrying out the method.
In order to achieve the above objects, according to the first aspect of the present invention, there is provided an electric-discharge surface treatment method in which a compressed powder electrode obtained by compression-molding of metal powder, metal compound powder, or ceramic powder, or a metal electrode is used as an electrode, and pulsed electric discharge is generated between the electrode and a material to be treated so that a hard coating composed of an electrode material or a substance obtained by reaction of the electrode material in response to energy of the electric discharge is formed on a surface of the material to be treated; characterized in that the method uses an electrode in which carbon or graphite powder, or a substance for producing carbon in response to energy of electric discharge is mixed into the electrode material.
Further, according to a second aspect of the present invention, there is provided, in an apparatus for electric-discharge surface treatment in which pulsed electric discharge is generated between an electrode and a material to be treated so that a hard coating comprising an electrode material or a substance obtained by reaction of the electrode material in response to energy of the electric discharge is formed on a surface of the material to be treated, an electrode for electric-discharge surface treatment characterized in that the electrode comprises a metal, a metal compound, or a mixture in which carbon or graphite powder, or a substance for producing carbon in response to energy of electric discharge is mixed into ceramics powder.
Further, according to a third aspect of the present invention, there is provided an electric-discharge surface treatment method in which a compressed powder electrode obtained by compression-molding of metal powder, metal compound powder, or ceramic powder, or a metal electrode is used as an electrode, and pulsed electric discharge is generated between the electrode and a material to be treated so that a hard coating composed of an electrode material or a substance obtained by reaction of the electrode material in response to energy of the electric discharge is formed on a surface of the material to treated; characterized in that the method uses an electrode in which carbon, graphite, or a substance for producing carbon in response to energy of electric discharge is mixed into the metal material.
According to a fourth aspect of the present invention, the electric-discharge surface treatment method is characterized in that a material of the electrode is titanium powder or a ititanium compound.
According to a fifth aspect of the present invention, the electrode for the electric-discharge surface treatment is characterized in that the material of the electrode is titanium powder or a titanium compound.
According to a sixth aspect of the present invention, there is provided an electric-discharge surface treatment apparatus in which a compressed powder electrode obtained by compression-molding of metal powder, metal compound powder, or ceramic powder, or a metal electrode is used as an electrode, and pulsed electric discharge is generated between the electrode and a material to be treated so that a hard coating comprising an electrode material or a substance obtained by reaction of the electrode material in response to energy of the electric discharge is formed on a surface of the material to be treated, characterized in that the apparatus comprises: an electrode in which carbon or graphite powder, or a substance for producing carbon in response to energy of electric discharge is mixed into metal powder, metal compound powder, or ceramic powder; a power supply unit for generating pulsed electric discharge between the electrode and a material to be treated; and treatment liquid supply means for supplying water as treatment liquid between the electrode and the material to be treated.